[Buildroot] [PATCH] system: Fix for NFS booting with interface config via DHCP

[Trent Piepho]

On Mon, 2015-11-09 at 00:44 +0100, Arnout Vandecappelle wrote:
> >>
> >>  However, why don't we just check if the interface is already up? Like
> >> ip link show $IFACE | cut -d ' ' -f 3 | grep -q UP
> > 
> > It's currently ok to call ifup on an interface that's already up.  It
> > will reconfigure it.  The interface, while up, might not have been
> > assigned an ip.
> > 
> > It wouldn't be tied to NFS at that point either.
> 
>  Right, so your approach is better then.
> 
>  BTW are we sure that /proc/mounts contains the IP address and not the host name?

I believe the nfsroot mount option only allows IP addresses and not
hostnames.  Since the kernel would have to do the DNS lookup.  And the
kernel docs say "<server-ip>", which seems to imply only an IP will
work.  It didn't work when I tried it.  And the busybox mount command
appears to only accept an IP ("mount: bad address 'hostname'").

But the util linux mount does accept a hostname and it does show up
in /proc/mounts as a hostname.

So you can get a hostname, but I don't think it's possible in a NFS root
case.  The mount options also in /proc/mounts will have addr=<ip>, which
is a way to get the numeric ip even if the hostname is present.  It does
make the sed parsing harder to get the value from there.